In a Twitter post, a respected Turkish ship spotter showed evidence that a Russian Kilo-class submarine allegedly passed through the Bosphorus, in violation of the Montreux Convention. At press time, we were unable to confirm the report independently, however, if true, the news would be very significant.
The Montreux Convention, officially known as The Montreux Convention Regarding the Regime of the Straits, was signed in 1936 and strictly regulates naval traffic through the Bosphorus, a narrow passage that separates Greece from Turkey and connects the Black Sea to the Mediterranean. Although merchant vessels enjoy unrestricted access to the Bosphorus and can pass without restriction, so-called vessels of war are subject to various restrictions, depending on their country of origin, where they were built or purchased, and their tonnage.
Regarding submarines specifically, the Turkish Ministry of Foreign Affairs states that, “only submarines belonging to riparian states can pass through the Turkish Straits, for the purpose of rejoining their base in the Black Sea for the first time after their construction or purchase, or for the purpose of repair in dockyards outside the Black Sea.” This crafty submarine appears to be acting in violation of this clause.